In prior art methods the frogs are formed during the slipforming process by pressing indentations with a tooth wheel or a tooth belt mat into the sides of the formed element.
A disadvantage of the prior art technique is that difficulty is often encountered when the desired frog shape is formed by pressing because the additional compression of the concrete is counteracted by the binding forces of the compacted and sheared concrete, which tend to retain the original form of the element, consequently inhibiting the forming of frogs with a desired depth of indentations. Also, the area surrounding the frog indentations tends to raise from the imposed pressure, leading to a deformed shape in the sides of the element. Additionally, the prior art technique makes it difficult to change the depth or mutual distance of frogs as changing of the pressing roller or belt mat is required. Achieving a desired frog depth may be impossible with the conventional technique because a deeper frog depth requires a high compressing force, and excessive compression will break the hollow-core construction.
SUMMARY OF THE INVENTION
The present invention aims to overcome the disadvantages of the aforementioned technique, and to achieve a completely novel method for the fabrication of frogs in hollow-core elements.
The invention is based on forming the frogs in the element by removing cast concrete from the elements by a reciprocative scraping action.
More specifically, the method in accordance with the invention is characterized by forming frogs in the sides of a slipformed concrete element, especially a hollow-core slab, in which the frogs are formed by removing cast concrete from the sides of the element by a reciprocation action.
Furthermore, the present invention provides for an apparatus in which frogs are formed in the sides of a slipformed concrete element, especially a hollow-core slab. This apparatus comprises support members which may be reciprocated parallel to the side of the element, a scraper and a transfer means.
The invention provides appreciable benefits.
The frog-forming apparatus in accordance with the present invention can be mounted to allow the continuous visual monitoring of its operation. The shape, depth, and mutual distance of the frogs is freely adjustable, in addition to the possibility of discontinuing the frog-forming process when required.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.